The present invention relates to an exhaust gas recirculation system in an internal combustion engine, and, more particularly, to an exhaust gas recirculation system having a turbocharger with two compressor wheels and a turbine having a variable intake nozzle.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. Likewise, the recirculated exhaust gas is preferably reintroduced to the intake air stream downstream of the compressor and air-to-air after cooler (ATAAC). Reintroducing the exhaust gas downstream of the compressor and ATAAC is preferred due to the reliability and maintainability concerns that arise if the exhaust gas passes through the compressor and ATAAC. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey), which is assigned to the assignee of the present invention.
It is also known to provide a turbocharger with a single turbine wheel and two compressor wheels. The turbine wheel is mechanically coupled with and rotatably drives each of the compressor wheels. One of the compressor wheels is used to compress combustion air received from the ambient environment, and the other compressor wheel is used to compress exhaust gas received from an exhaust manifold. By compressing the exhaust gas, the exhaust gas may be effectively mixed with the combustion air for recirculation to the intake manifold of the internal combustion engine.
Dependent upon certain operating conditions associated with the diesel engine, it may be desirable to provided a richer or leaner mixture of the exhaust gas within the combustion air which is transported to the intake manifold. One known technique for controlling the amount of exhaust gas which is mixed with the combustion air utilizes controllably actuatable valves which interconnect the exhaust manifold with the compressor which receives the exhaust gas. The flow of exhaust gas to the second compressor can be completely shut off, or can be controlled on a timed basis to provide a desired average flow of exhaust gas which mixes with the combustion air. Another known technique is to provide a bypass fluid conduit associated with the combustion air or exhaust gas. A controllably actuatable butterfly valve or the like is positioned within the bypass fluid conduit and controlled to in turn control the amount of exhaust gas which mixes with the combustion air. Although such systems are effective to control exhaust gas recirculation within the diesel engine, they usually require that additional structure in the form of sensors, conduits, valves and associated controllers be added to the internal combustion engine.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine comprises at least one exhaust manifold and at least one intake manifold. A turbocharger includes a turbine, a first compressor and a second compressor. The turbine is connected with the exhaust manifold and has a controllable variable nozzle. The first compressor and the second compressor each are connected with and driven by the turbine. The first compressor has an inlet for receiving combustion air and an outlet. The second compressor has an inlet connected with each exhaust manifold and an outlet. A mixer interconnects the first compressor outlet and the second compressor outlet with the intake manifold. A controller is connected with and controls operation of the turbine variable nozzle, dependent upon an operating characteristic associated with the second compressor.
In another aspect of the invention, an exhaust gas recirculation system in an internal combustion engine including an exhaust manifold and an intake manifold comprises a turbocharger with a turbine, a first compressor and a second compressor. The turbine is configured for connection with the exhaust manifold and has a controllable variable nozzle. The first compressor and the second compressor each are connected with and driven by the turbine. The first compressor has an inlet for receiving combustion air and an outlet. The second compressor has an inlet configured for connection with the exhaust manifold and an outlet. A mixer is connected with each of the first compressor outlet and the second compressor outlet. A controller is connected with and controls operation of the turbine variable nozzle, dependent upon an operating characteristic associated with the second compressor.
In yet another aspect of the invention, a method of operating an exhaust gas recirculation system in an internal combustion engine comprises the steps of: providing an exhaust manifold and an intake manifold; providing a turbocharger including a turbine, a first compressor and a second compressor, the turbine configured for connection with the exhaust manifold and having a controllable variable nozzle, the first compressor and the second compressor each being connected with and driven by the turbine, the first compressor having an inlet for receiving combustion air and an outlet, the second compressor having an inlet connected with the exhaust manifold and an outlet; providing a controller connected with the turbine variable nozzle; flowing exhaust gas from the exhaust manifold to each of the turbine variable nozzle and the second compressor inlet; and controlling operation of the turbine variable nozzle, dependent upon an operating characteristic associated with the second compressor.